ISM, ISMe, and QSM11 – 001-043   Piston

All M Series engines are equipped with articulated pistons.

The articulated piston is a two-piece piston consisting of a forged-steel crown and an aluminum skirt.

A closed chamber oil gallery is located on the underside of the crown of the piston to provide more oil contact with the piston and give better piston cooling. Piston cooling nozzle targeting is critical because of the closed chamber oil gallery.

The piston and connecting rod must be removed as an assembly.

• Remove the piston and connecting rod. Refer to Procedure 001-054 in Section 1.

Disassemble the piston and connecting rod assembly. Refer to Procedure 001-054 in Section 1.

Inspect the piston rings. Refer to Procedure 001-047 in Section 1.

WARNING  When using solvents, acids, or alkaline materials for cleaning, follow the manufacturer’s recommendations for use. Wear goggles and protective clothing to reduce the possibility of personal injury.

CAUTION  Be sure the cleaning solvent is approved for aluminum. Damage to the pistons can result if the wrong solution is used.

Allow the pistons to soak for a minimum of 30 minutes in a tank containing an approved cleaning solvent for aluminum.

Use a hot, soapy solution and a nonmetallic brush to remove carbon deposits.

WARNING  When using a steam cleaner, wear safety glasses or a face shield as well as protective clothing. Hot steam can cause serious personal injury.

WARNING  Wear appropriate eye and face protection when using compressed air. Flying debris and dirt can cause personal injury.

Use steam to clean the pistons.

Dry with compressed air.

Inspect the piston bowl (1) and crown piston pin bore (2) for cracks or damage.

Do not use pistons with cracks. If the crown is cracked, it must be replaced.

Inspect the piston gallery cover plate in the piston crown for cracks or looseness.

If the gallery is cracked or loose, the piston crown must be replaced.

Inspect the piston skirt pin bore (1) and sides (2) for cracks or damage.

Do not use pistons with cracks. If the skirt is cracked, it must be replaced.

The ring groove can be inspected with a new ring and a feeler gauge.

Hold a new ring in the groove even with the outside diameter of the piston. Install a 0.15-mm [0.006-in] feeler gauge. If the feeler gauge enters the groove without resistance, there is too much wear. Replace the piston.

Measure the piston pin bore inside diameter.

Articulated Piston Pin Bore Inside Diameter (Crown)

Articulated Piston Pin Bore Inside Diameter (Skirt)

Measure the piston pin outside diameter and length.

Piston Pin Outside Diameter

Piston Pin Length

• Assemble the piston and connecting rod. Refer to Procedure 001-054 in Section 1.

The piston and connecting rod must be installed as an assembly.

• Install the piston and connecting rod assembly. Refer to Procedure 001-054 in Section 1.

If the malfunction resulted in coolant, oil, excessive fuel. or excessive black smoke entering the exhaust system, the aftertreatment system must be inspected. Refer to Procedure 014-013 in Section 14.